Activation of lymphocytes by BAT and anti CTLA-4: Comparison of binding toT and B cells

In this study we compare the binding and immune stimulatory properties of B AT and anti CTLA-4 monoclonal antibodies (mAbs). Both antibodies were previ ously shown to manifest effective immune responses against tumor cells. We have described that BAT antibody, produced against Daudi, a B lymphoblastoi d cell line, binds and activates T cells. In this paper we demonstrate that anti CTLA-4, produced against the T-cell activation determinant CTLA-4, bi nds also to B lymphoblastoid cell lines like Daudi and Raji. Both antibodie s do not bind resting B cells. BAT binds resting T lymphocytes as well as a ctivated T lymphocytes, whereas anti CTLA-4 binds only activated T cells. C ompetitive binding experiments indicate that the binding sites of BAT and a nti CTLA-4 on activated T cells are distinct. We have studied the in vitro stimulatory effect of BAT and anti CTLA-4 on lymphocytes cultured with or w ithout tumor cells. In contrast to BAT that increased the proliferation of lymphocytes that have been cultured with tumor cells, anti CTLA-4 did not s ynergize with tumor cells to enhance lymphocyte proliferation. (C) 1999 Els evier Science B.V. All rights reserved.